1. Field of the Invention
The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to a method of fabricating an electronic component package having a heat transfer structure.
2. Description of the Related Art
As is well known to those skilled in the art, an electronic component such as an integrated circuit generated heat during operation. To prevent failure of the electronic component, it was important to prevent the electronic component from becoming overheated during operation.
To prevent the electronic component from becoming overheated, a heat sink was employed within the package, which housed the electronic component. In this manner, heat generated by the electronic component was transferred to the heat sink and dissipated to the ambient environment. This maintained the temperature of the electronic component at a suitable level.
To maximize the effectiveness of the heat sink, it was desirable to expose the heat sink directly to the ambient environment. Stated another way, it was desirable to prevent the heat sink from being enclosed within the molded plastic encapsulant. This was because the molded plastic encapsulant had a substantially lower heat transfer coefficient than the heat sink, e.g., copper, and thus impeded heat transfer from the heat sink to the ambient environment.
To prevent the heat sink from being enclosed within the molded plastic encapsulant, it was important that the mold half press firmly against the heat sink during encapsulation. In this manner, a tight seal was formed between the heat sink and the mold half to prevent the molded plastic encapsulant from leaking between the heat sink and the mold half. Molded plastic encapsulant, which leaks between the heat sink and the mold half, is commonly referred to as flash.
In the prior art, the heat sink was sandwiched between the mold half and leads of a lead frame. When the mold was closed, the leads were deflected slightly creating tensile force in the leads. This tensile force acted to press the heat sink tightly against the mold half thus preventing flash from forming around the heat sink.
Alternatively, in Weber, U.S. Pat. No. 5,609,889, the mold was provided with a bias plug that exerted pressure on the heat sink and prevented flash from forming around heat sink. The bias plug pressed the heat sink against a printed wiring board type substrate.
As set forth above, to prevent flash from forming around the heat sink, the heat sink was pressed against either leads of a lead frame or against a printed wiring board type substrate. However, these techniques only allowed the heat sink to remove heat from the lower surface, sometimes called the back-side surface, of the electronic component.
The heat sink could not be pressed against the upper surface, sometimes called the front-side surface, of the electronic component since the electronic component was relatively fragile and would be damaged or destroyed from the heat sink pressure. However, it is desirable to remove heat from the upper surface of the electronic component in certain applications.
In accordance with the present invention, an RF shielded package includes a heat sink having a plurality of spring elements. The spring elements serve several functions.
One function of the spring elements is to press the heat sink against the mold half during encapsulation to prevent the encapsulant, e.g., molded plastic encapsulant, from leaking between the heat sink and the mold half. This insures that an upper surface of the heat sink is exposed to the ambient environment and not covered by flash thus maximizing heat transfer from the RF shielded package.
Further, since the spring elements press against the substrate and not against the electronic component, the heat sink does not damage or destroy the electronic component. This allows the heat sink to be thermally connected directly to the upper surface of the electronic component.
Another function of the spring elements is to ground the heat sink. More particularly, the spring elements pressed directly on and are electrically connected to ground traces on an upper surface of the substrate. During use, the ground traces and thus the heat sink are electrically connected to a reference voltage source, e.g., ground. Accordingly, the heat sink forms a grounded shield above the electronic component and protects the electronic component from RF radiation.
These and other features and advantages of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings.